The central hypothesis of this proposal is that there are age-related perturbations of homeostasis in the central nervous system (CNS) that account for the cognitive deficits and increased incidence of brain tumors reported for the very aged human population. These homeostatic failures are likely to reflect the altered activity of intercellular signals such as the nerve growth factor protein (NGF), a member of the neurotrophin family of factors, in CNS neurons and glia, respectively. It is proposed that a critical component of these homeostatic processes is the interaction of NGF with glucocorticoids in terms of expression of NGF receptors (NGFR). NGFR have two components: p75 NGFR and p140 prototrk. The intracellular elements of NGF action act in part through the induction of early response genes (ERGs). In order to test this hypothesis, the NGF induction of NGFR MRNA species in rodent glial cells will be characterized through the use of equilibrium 125I-NGF binding assays, 125I-NGF protein crosslinking to NGFR species, Northerns, polymerase chain reaction (PCR), and ribonuclease protection assays to measure glucocorticoid receptor (GR), ERG, p75 NGFR and p 140 prototrk MRNA levels. The interactions between NGF and glucocorticoids, as they affect NGF, NGFR, GR, and ERG expression in vitro and in rat aged CNS will be defined. The effects of NGF on glial proliferative activity will be measured. The sequelae of transcriptional events associated with ERG induction by NGF in glia will be contrasted to NGF induction of ERGs in neurons and mitogen induced ERG expression in glia. Lastly, age- associated changes in the parameters established above will be determined thorough the combined use of tissue culture and in vivo approaches with the aim of defining molecular events disrupted by aging that disturb the homeostatic processes regulated by NGF action. Animals to be used will be 3, 18, and 30 month old BNXF1 rats. An eventual goal of these studies is to integrate knowledge on the roles of growth factors, steroids, and neurotransmitters in CNS homeostatic mechanisms. A better understanding of age-associated neuropathology relevant to degenerative neurological diseases and brain neoplasia will result from these studies.